The present invention relates to a surface inspection apparatus for inspecting foreign objects attached on a substrate such as a wafer and flaws on the surface of the substrate in a process to manufacture semiconductor device. In particular, the present invention relates to a surface inspection apparatus provided with an inspection stage, on which centering of the substrate can be performed.
Various types of semiconductor devices are manufactured by forming a number of semiconductor elements on a semiconductor wafer such as silicon. With the progress in high-density integration, the fabricating process is being changed to produce more and more micro-sized products. To increase the production yield, wafers with large diameters are more and more being produced.
With the progress of high-density integration and with the production of more and more micro-sized products, foreign objects attached on the wafer or presence of flaws on the wafer surface exert big influence on product quality and production yield. For this reason, inspection process is now incorporated into the process to manufacture the semiconductor products. Surface inspection is performed on the wafers by using a surface inspection apparatus, and attaching condition of foreign objects and presence or absence of flaws on the surface of wafers are inspected.
A surface inspection apparatus for wafers has an inspection stage to hold wafers. The inspection stage is rotated at high speed. Laser beams are projected to the surface of the wafer rotated at high speed, and the surface is scanned by the laser beams in circumferential direction. The laser beams reflected by the wafer surface are received, and attachment of foreign objects or presence or absence of flaws on the surface are detected from the reflecting conditions.
As described above, wafers with increasingly larger diameter are now produced. On the other hand, there is such demand that inspection time is gradually reduced to improve the productivity. The rotating speed of wafers during inspection is also increased. Therefore, high centrifugal force is applied on the held wafer when the wafer is inspected. Also, the amount of decentering between the wafer center and the rotation center of the inspection stage gives big influence on the centrifugal force to be applied on the wafers.
Further, when foreign objects or flaws are detected on the surface of wafer, the position (i.e. coordinates) of the foreign object or flaw is given by using the center of wafer and an orientation flat or notch as reference. The center of wafer is determined by using the edge as reference. The edge of the wafer is held on the surface inspection apparatus and is detected under rotating condition. If the amount of decentering of the wafer is high, the wafer edge is moved extensively, and it is difficult to detect the edge accurately. The accuracy of the reference coordinates is worsened and this may cause damage on the wafer. As a result, the accuracy of information on the position of the detected foreign object or flaw is also decreased.
In this connection, the center of the wafer must be accurately aligned with the rotation center of the inspection stage when the wafer is held on the surface inspection apparatus.
In the past, a centering device has been used in addition to the surface inspection apparatus for the centering of the wafer. Wafer centering is performed by using the centering device, and then, the wafer is shifted to the surface inspection apparatus by a wafer transportation mechanism. Thus, the centering of the wafer on the centering device is reflected when the wafer is held by the surface inspection apparatus.
However, the wafer centering as practiced in the past has the following disadvantages:
The wafer centering is performed by using the centering device, which is separately furnished. This means that the centering device is needed and also a process for centering is required. Error may occur when the process is shifted from the centering device to the surface inspection apparatus.
Positioning between the surface inspection apparatus and the centering device must be carried out via a wafer transportation mechanism, and this causes problems such as difficulty in adjustment.
As a surface inspection apparatus for carrying out position alignment, centering, etc. of wafers before inspection, the apparatuses disclosed in the Japanese Patent Publications 2729297 and 2846423 have been known, for instance.